Bruxism, a type of mandibular dysfunction characterized by constant, execessive grinding of teeth, is not well understood. Although a number of causal factors have been suggested, there is general agreement that emotional stress plays an important role in moast instances of this condition. Additionally , during periods of bruxing, the protective reflexes which prevent abnormal stresses upon the teeth by activating jaw opening are absent. We plan to analyze the role of the hypothalamic-midbrain continuum in bruxism. Evidence in support of the view that the hypothalamic-midbrain continuum modulates bruxing behavior is derived rron the role of the hypothalamus in aggressive behaviors adn its influence upon jaw reflexes. However, the anatomical and physiological mechanisms through which the hypothalamic-midbrain continuum controls orofacial responses have yet to be identified. The objective of these proposed experiments will be to identify the anatomical pathways by which this region controls orofacial behaviors. Experimental techniques which employ histochemical tracers and autoradiographic procedures that label the cytoplasmic processes (cell bodies and axons) of neurons will be used to map the pathways. Phase I: A tritiated aminoacid will be injected into midbrain sites which upon stimulation can modify jaw reflexes in cats. This procedure will permit mapping of the pathways from the midbrain to the trigeminal nucleus and related structures. Phase II: To confirm our observations noted in Phase I, a retrograde tracer (Horseradish peroxidase, HRP) will be utilized. Sites having previously been identified as receiving projections from the midbrain will be injected with HRP and the labelled cell bodies of origin of this pathway will be identified. Phase III: 14C-2-deoxyglucose maps of the lower brainstem regions activated following stimulation of sites from which jaw reflexes can be modified will be constructed. By utilizing three independent anatomical techniques, it is hoped that these experiments will provide a better understanding of the structural mechanisms by which the hypothalamic-midbrain continuum can control jaw reflexes.